The Mexican wolf (Canis lupus baileyi), also known as the lobo, is a subspecies of gray wolf native to the Sierra Madre and the surrounding area of western Mexico, though its range once included the southeastern United States. It is the smallest of North America's gray wolves,[2] and is similar to C. l. nubilus, though it is distinguished by its smaller, narrower skull and its darker pelt, which is yellowish-gray and heavily clouded with black over the back and tail.[3] Its ancestors were likely the first gray wolves to enter North America after the extinction of the Beringian wolf, as indicated by its southern range and basal physical and genetic characteristics.[4]

Though once held in high regard in Pre-Columbian Mexico,[5] it is the most endangered gray wolf in North America, having been extirpated in the wild during the mid-1900s through a combination of hunting, trapping, poisoning and digging pups from dens. After being placed on the Endangered Species Act in 1976, captive-bred Mexican wolves were released into recovery areas in Arizona and New Mexico in the late 1990s in order to assist the animals' recolonization of their former historical range.[6]

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First described as a distinct subspecies in 1929 by Edward Nelson and Edward Goldman on account of its small size, narrow skull and dark pelt,[7] genetic and morphological studies indicate that the Mexican wolf is the most basal and genetically distinct of North American gray wolves, being more closely related to Old World wolves rather than other New World subspecies.[4] Its ancestors were likely the first gray wolves to cross the Bering Land Bridge into North America during the Pleistocene after the extinction of the Beringian wolf,[8] colonizing most of the continent until pushed southwards by the newly arrived ancestors of C. l. nubilus.[4]

An analysis of controlled-region haplotypes of the mitochondrial DNA and sex chromosomes of Mexican wolves by Uppsala University detected the presence of coyote markers in some specimens. However, these markers were absent in captive Mexican wolf populations, thus suggesting that some male wolves from remnant wild populations began mating with female coyotes and coywolf hybrids, later backcrossing to other male wolves. Analysis on Texan coyote haplotypes also detected the presence of male wolf introgression, such as wolf Y-chromosomes in some of the male coyotes. In an extremely rare case, the study found that one coyote out of seventy individuals from Texas was discovered to carry a mtDNA haplotype derived from a female Mexican wolf, thus indicating that a male coyote had also managed to breed with a female Mexican wolf in the wild. The Mexican wolf may be the only gray wolf in the southern states besides domestic and feral dogs to have hybridized with coyotes.[9]

In tests performed on a sample from a taxidermied carcass of what was initially labelled as a chupacabra, mitochondrial DNA analysis conducted by Texas State University professor Michael Forstner showed that it was a coyote. However, subsequent analysis by a veterinary genetics laboratory team at the University of California, Davis concluded that, based on the sex chromosomes, the male animal was a coyote–wolf hybrid sired by a male Mexican wolf.[10][11] It has been suggested that the hybrid animal was afflicted with sarcoptic mange, which would explain its hairless and blueish appearance.[10]

The Aztec god Xolotl, depicted here in the 15th century Codex Fejervary-Mayer, may have been based on the Mexican wolf rather than a dog as once believed.[5]

The Mexican wolf was held in high regard in Pre-Columbian Mexico, where it was considered a symbol of war and the Sun. In the city of Teotihuacan, it was common practice to crossbreed Mexican wolves with dogs to produce temperamental, but loyal, animal guardians. Wolves were also sacrificed in religious rituals, which involved quartering the animals and keeping their heads as attire for priests and warriors. The remaining body parts were deposited in underground funerary chambers with a westerly orientation, which symbolized rebirth, the Sun, the underworld and the canid god Xolotl.[5] The earliest written record of the Mexican wolf comes from Francisco Javier Clavijero's Historia de México in 1780, where it is referred to as Cuetzlachcojotl, and is described as being of the same species as the coyote, but with a more wolf-like pelt and a thicker neck.[12]

There was a rapid reduction of Mexican wolf populations in the southwestern USA from 1915-1920; by the mid-1920s, livestock losses to Mexican wolves became rare in areas where the costs once ranged in the millions of dollars.[13]Vernon Bailey, writing in the early 1930s, noted that the highest Mexican wolf densities occurred in the open grazing areas of the Gila National Forest, and that wolves were completely absent in the lower Sonora. He estimated that there were 103 Mexican wolves in New Mexico in 1917, though the number had been reduced to 45 a year later. By 1927, it had apparently become extinct in New Mexico.[3] Sporadic encounters with wolves entering Texas, New Mexico and Arizona via Mexico continued through to the 1950s, until they too were driven away through traps, poison and guns. The last wild wolves to be killed in Texas were a male shot on December 5 1970 on Cathedral Mountain Ranch and another caught in a trap on the Joe Neal Brown Ranch on December 28. Wolves were still being reported in small numbers in Arizona in the early 1970s, while accounts of the last wolf to be killed in New Mexico are difficult to evaluate, as all the purported "last wolves" could not be confirmed as genuine wolves rather than other canid species.[13]

The Mexican wolf persisted longer in Mexico, as human settlement, ranching and predator removal came later than in the southwestern USA. Wolf numbers began to rapidly decline during the 1930s-1940s, when Mexican ranchers began adopting the same wolf-control methods as their American counterparts, relying heavily on the indiscriminate usage of 1080.[13]

A pair of Mexican wolves with pups at Sevilleta Wolf Management Facility

The Mexican wolf was listed as endangered under the Ecological Society of America in 1976, with the Mexican Wolf Recovery Team being formed three years later by the United States Fish and Wildlife Service. The Recovery Team composed the Mexican Wolf Recovery Plan, which called for the reestablishment of at least 100 wolves in their historic range through a captive breeding program. Between 1977 to 1980, four males and a pregnant female were captured in Durango and Chihuahua in Mexico to act as founders of a new "certified lineage". By 1999, with the addition of new lineages, the captive Mexican wolf population throughout the US and Mexico reached 178 individuals. These captive-bred animals were subsequently released into the Apache National Forest in eastern Arizona, and allowed to recolonize east-central Arizona and south-central New Mexico, areas which were collectively termed the Blue Range Wolf Recovery Area (BRWRA). The Recovery Plan called for the release of additional wolves in the White Sands Wolf Recovery Area in south-central New Mexico, should the goal of 100 wild wolves in the Blue Range area not be achieved.[6]

By late 2012, it was estimated that there were at least 75 wolves and four breeding pairs living in the recovery areas, with 27% of the population consisting of pups. Since 1998, 92 wolf deaths were recorded, with four occurring in 2012; these four were all due to illegal shootings.[14]

Releases have also been conducted in Mexico, and the first birth of a wild wolf litter in Mexico was reported in 2014.[15]

A study released by the U.S. Fish and Wildlife Service in February 2015 shows a minimum population of 109 wolves in 2014 in southwest New Mexico and southeast Arizona, a 31 percent increase from 2013.[16]